The use of a metallized plastic strip embedded within currency paper as a security thread for counterfeit deterrence is described within U.S. Pat. Nos. 4,652,015 and 4,761,205, which Patents are incorporated herein for purposes of reference. The security thread is virtually undetected under reflected light while being readily discerned under transmitted light to verify its presence.
In commercial situations where verification of currency bills is required, the receiver of the currency bill should subject the currency to a relatively intense light source to detect the security thread under transmitted light. With large queues of customers at a bank or supermarket, as well as in places of low level illumination such as bars and restaurants it is difficult to visually inspect the corresponding large number of currency bills. It would be advantageous therefore to have some means of automatically determining the presence of the requisite security thread and confirming authenticity to the teller or cashier.
U.S. Pat. No. 4,524,276 entitled "Apparatus for Detecting a Security Thread Embedded in a Paper-Like Material" describes an infrared radiation source and two infrared radiation detectors used to determine whether or not a security threads is embedded in the paper-like material and also what the detected security material is made of.
Countries outside of the United States that employ plastic or metal security threads embedded in their paper currency, require that the presence of such security threads be ascertained under transmitted light such as described in the aforementioned U.S. Pat. No. 4,524,276. In accordance with the United States requirement that the currency security thread be detected under transmitted light and not seen under reflected light, both reflective and transmissive determinations must be made for complete verification of the currency.
One purpose of the instant invention therefore, is to provide automatic means for determining currency verification by both reflective and transmissive tests and for providing immediate indication of the results thereof.